After being defeated by Quartermaster Rackum, I teamed up with another player and we had to fight two battles, neither having the quartermaster present. We decided to try again, and the quartermaster appeared. After a hit, a zebra cheat was active, despite the fact that there was no zebra present. Then, he disappeared along with a corrupted rhino.
I don't know if this is just a temporary thing or if that dungeon has bugs. My companion (I forgot the first name, but the last was strongbreaker) suggested that we try again later, so I might try again and see if it was really bugged.
